Add link checking and fix missing image

.github/workflows/PR_link_checker.yml

@@ -0,0 +1,15 @@
+name: Check links during PRs
+
+on: 
+  pull_request:
+
+jobs:
+  markdown-link-check-pr:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@master
+    - uses: gaurav-nelson/github-action-markdown-link-check@v1
+      with:
+        use-quiet-mode: 'yes'
+        check-modified-files-only: 'yes'
+        base-branch: 'main'

.github/workflows/cron_link_checker.yml

@@ -0,0 +1,15 @@
+name: Check links periodically
+
+on: 
+  schedule:
+  # Run Friday at 3:15pm
+  - cron: "15 15 * * FRI"
+
+jobs:
+  markdown-link-check-cron:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@master
+    - uses: gaurav-nelson/github-action-markdown-link-check@v1
+      with:
+        use-quiet-mode: 'yes'

nibble/build_guide_en.md

@@ -53,7 +53,7 @@ Seriously, thank you! The NIBBLE has been a passion project of mine over the pas
 | --------------------- | -------- | ------------------------------------------------------------------------------------ |
 | 1N4148 Diode          | 73       | ![](https://github.com/nullbitsco/docs/raw/main/nibble/build_guide_img/image003.jpg) |
 | 0.1μF Capacitor       | 2        | ![](https://github.com/nullbitsco/docs/raw/main/nibble/build_guide_img/image005.jpg) |
-| 330Ω Resistor         | 3        | ![]()                                                                                |
+| 330Ω Resistor         | 3        | ![](https://www.newark.com/productimages/standard/en_US/4415447.jpg)                                                                                |
 | IC Socket             | 2        | ![](https://github.com/nullbitsco/docs/raw/main/nibble/build_guide_img/image007.jpg) |
 | IC (74HC138N)         | 2        | ![](https://github.com/nullbitsco/docs/raw/main/nibble/build_guide_img/image009.jpg) |
 | Reset Switch          | 1        | ![](https://github.com/nullbitsco/docs/raw/main/nibble/build_guide_img/image011.jpg) |